Do Fish Have an Absolute Sense of Light Intensity?
The appreciation of intensity is based on a number of physiological characteristics. One of the most striking attributes of the sense organs, especially of sight and hearing, is their versatility in terms of the range of intensity which they can appreciate, of the order of 12 logarithmic units from the minimum threshold to the maximum level “bearable”. Fechner’s Law states that the “sensation” is proportional to the logarithm of the stimulus intensity (Fig. 1A), which means that visual or auditory perception goes through a process opposite to amplification. Putting it very simply, the sensory system in some way reduces the range of “sensation” perceivable from about one million million to only 12 times. In the case of vision the versatility of the eye is aided by the presence in many animals of rods and cones with a mechanism of dark-and light-adaptation.
KeywordsLight Intensity Vertical Migration Visual Pigment Diel Vertical Migration Pacific Salmon
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